Injector Analysis from the Regulator

To perform this test disconnect the vacuum hose from the fuel pressure regulator and plug the vacuum hose. Then place the reducer hose on the FirstLook sensor and connect it to channel A of the scope using the BNC to BNC lead as shown on Figure 1.0. Now connect the reducer hose and FirstLook sensor to the regulator port as shown in Figure 1.1.

Channel B can be used for triggering, this can be achieved by using one of the injectors (voltage or current) or the secondary ignition pickup lead.

This waveform was taken using injector number 1 as trigger on channel B and the FirstLook sensor signal on channel A. Let us consider what happens when an injector is opened, as it affects the regulator. The sudden drop in fuel pressure causes a fluctuation in the regulator. The fuel pump then compensates to fill the void left by the exiting fuel, thus returning the regulator to its starting position. In this test we can view the resulting waveform caused by this action. Notice the sharp change as the injector is opened followed by the compensation curve back to the base state.

The waveform seen will depend on the injector firing pattern. In this case the injectors are sequential (each injector fires at a preset time before the ignition). In the above example it can be seen that the drop in fuel pressure for number 1 cylinder is slightly less than the others, this may suggest a blocked injector.